Method of forming an integral colored anodic oxide on aluminum pressure die castings

ABSTRACT

An integral colored anodic oxide film free from irregular patterns of metal flow, seams and cold shuts can be formed on die castings by subjecting the surface of pressure die castings of an aluminum alloy comprising 0.1 - 1.3 percent by weight of chromium, 0.2 - 3.4 percent by weight of manganese, said chromium and manganese being present in the amounts which are within the area of quadrilateral ABCD shown in the FIGURE, up to 0.3 percent by weight of impurities and the balance of aluminum, to roughening and brightening treatments, and thereafter subjecting thus treated products to anodizing treatment. Mechanical strength and castability of the alloy is further improved by addition of cobalt or zinc.

[451 Sept. 3, 1974 METHOD OF FORMING AN INTEGRAL COLORED ANODIC OXIDE ONALUMINUM PRESSURE DIE CASTINGS [75] Inventors: Kiyomi Yanagida; IsaoSatake, both of Nagoya, Japan [73] Assignee: Sumitomo Chemical CompanyLimited, Osaka, Japan [22] Filed: Feb. 18, 1972 [21'] Appl. No.: 227,593

[30] Foreign Application Priority Data 671,508 10/1963 Canada 204/58OTHER PUBLICATIONS The Surface Treatment of Al & Its Alloys by Wernicket a1., 3rd Ed., 1964, p. 56. Y 1

Primary Examiner-John H. Mack Assistant ExaminerR. L. Andrews Attorney,Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT An integralcolored anodic Oxide film free from irreg- Feb. 24, 1971 Japan 46-9521ular patterns of metal flow eams and cold shuts can May 18, 1971 P46-33323 be formed on die castings by subjecting the surface of May 19,1971 Japan 46-34264 pressure die castings of an aluminum alloycomprising 0.1 1.3 percent by weight of chromium, 0.2 3.4 U-S- percentof manganese aid chromium and manganese being present in the amounts areFleld of Search 29, the area of quadrilateral hown in the FIGURE, up to0.3 percent by weight of impurities References Clted and the balance ofaluminum, to roughening and' FOREIGN PATENTS OR APPLICATIONS brighteningtreatments, and thereafter subjecting thus 671,508 10/1963 Canada 204/58treated Products 10 anodizing treatment Mechanical 470,734 8/1937 GreatBritain... 204/58 Strength and castability of the alloy is further im-401,097 l/1965 Japan 204/58 proved by addition of cobalt or zinc. 40,4121/1965 .lapan.... 204/58 o 40,413 l/1965 Japan 204/58 9 Clams, 1 DrawmgFlgure 0 v l 0 a 5 z 5' 671%) PAIENIEDSEP 3 914 3.883.484

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METHOD OF FORMING AN INTEGRAL COLORED ANODIC OXIDE ON ALUMINUM PRESSUREDIE CASTINGS conspicuously formed. Therefore, such products have notbeen able to be utilized for decoration which aims at uniformity ofsurface color. Beingdifferent from sand castings or permanent moldcastings, in the pro duction of the pressure die castings, melt ofaluminum alloy is pressure injected,-'namely, the melt is charged intodies under a'high pressure in turbulent flow state. Therefore, in thepressure die casting, opportunities for contacting the melt of aluminumalloy and air much more occasionally-occur than in sand casting methodsand permanent mold casting methods and hence oxide of aluminum formsirregularpatterns of metal flow and seams in the direction of the meltflow and cold shuts at joints where the melts collide with each other.Since these defects are contained on the surface and in the inner partof the die castings, anodizing treatment resultsin an unevenly coloredoxide film. In case of the conventionally known pressure die castingaluminum alloys, even if these irregular patterns of metal flow, seamsand cold shuts are physically or mechanically removed by buffing orblasting treatment before anodizing treatment, they are again formedwhen the die castings are subjected to chemical polishing and then toanodizing treatment. This phenomenon is especially clearly recognizedwith alloys which form relatively light colored anodic oxide film.

As the result of the inventors research on pressure die casting aluminumalloys and a method for surface treatment of the die castings, it hasbeen found that an integral and uniform colored anodic oxide film isformed by subjecting the products obtained by die casting the Al-Mn-Cralloys to suitable surface treatment. Hitherto, such alloys have beenknown as those for forming a colored anodic oxide film on wroughtproducts, for example, in Japanese Patent Publication No. 16218/63.However, such alloys have not been used as colored die castings fordecoration obtained by integral color anodizing (or self-coloranodizing), because the irregular patterns of metal flow, seams, andcold shuts cause unevenness of color.

The FIGURE is a graph which shows the composition ranges of chromium andmanganese in the alloy of the present invention.-

The present invention provides a method for forming an integralanduniform colored film on aluminum pressure die castings whichcomprises die casting by the known method an alloy comprising 0.1 1.3percent by weight of chromium, 0.2 3.4 percent by weight of manganese,said chromium and manganese being present in the amounts which arewithin the area of quadrilateral ABCD shown in FIG. 1, up to 0.3 percentby weight of impurities and the balance of aluminum, roughening thesurface of thus obtained die castings, subjecting the'products tobrightening treatment and thereafter subjecting the products to theanodizing treatment in the usual known methods, preferably in 2 aqueouselectrolyte containing 5 to 20 percent by weight of sulfuric acid.

When the chromium content in the alloy is less than 0.1 percent byweight, effective coloration is not attained. With increase of thecontent of chromium, yellowish color is increased, but the content ofhigher than 1.3 percent by weight is not preferred because it becomesnecessary to raise the melting temperature of the alloy during the diecasting procedure, whereby operation of pressure die casting becomesdifficult due to increase of oxidation loss of the aluminum alloy anddifficulty in parting from the pressure die casting dies.

Less than 0.2 percent by weight of manganese provides no effect oncoloration. With increase of the content of manganese, the anodic oxidefilm is rendered reddish. However, when the content exceeds 3.4 percentby weight, irregular patterns of metal flow, seams and cold shuts beginto, appear and it becomes difficult to obtain the desired integral anduniform anodic colored film. Therefore, the content of manganese shouldbenot more than 2.2 percent by weight to obtain especially uniformanodic colored film.

Furthermore, the contents of chromium and manganese should be present inthe amounts below the straight line connecting points A and B in FIG. 1and when the contents exceed the values shown by the line AB, a filmhaving uneven color is formed. An anodic oxide film having various colortones of from golden color to brown and reddish brown colors is obtainedby suitably controlling the contents of chromium and manganese withinsaid range. That is, when the weight ratio of manganese to chromium islower than about 1.3, the film turns yellowish brown, when it is about1.3 3, the film turns golden color or brown color and when it is higherthan about 3, the film turns reddish brown. A more uniform anddecorative colored anodic oxide film on aluminum pressure .die castingsis obtained by controlling chromium and manganese in the amounts whichare within the pentagonal area DEFGH shown in the FIGURE. Moreover,regarding iron and silicon contained in the alloy of the presentinvention as impurities, it is necessary that iron be up to 0.2 percentby weight and silicon be up to 0.1 percent by weight because they causethe film to have greyish black color and prevent coloration of alloyingelements added.

Furthermore, mechanical strength and castability of pressure die castingaluminum alloys can be improved by adding cobalt or zinc to the alloy.That is, addition of 0.005 0.8 percent by weight of cobalt can improvesoldering of the melt of aluminum alloy to dies for pressure die castingand prevent hot tear of the die castings. The soldering ofgeneralpressure die casting aluminum alloys is prevented by adding 0.6 1.0percent by weight of iron. However, in case of the alloy of the presentinvention, addition of more than 0.2 percent by weight of iron causesthe anodic oxide film to turn greyish black. Since removal of the diecastings from dies becomes easy by addition of cobalt, it becomespossible to obtain products of more complicated shape. The addition ofcobalt has the additional effect of increasing the mechanical strengthof the product without giving an adverse effect on the colored film. Inaddition, cobalt has an effect of reducing the anodizing treatment time,thereby improving working efficiency. When the content of cobalt islower than 0.005 percent by strength of die castings without givingadverse effect on color tone of the oxide film. For example, Brinellhardness of Al-0.5 percent Mn-0.3 percent Cr alloy is H 27, but when thealloy contains 5 percent of zinc, Brinell hardness of the alloy becomesH 31. As mentioned above, with increase of the mechanical strength ofdie casting alloy, prevention of deformation of the die castings duringparting from the dies and during handling can be expected. When contentof zinc is less than 0.1 percent by weight,there is attained no sucheffect and when it exceeds 5.0 percent by weight, irregular patterns ofmetal flow, seams and cold shuts appear in the anodic oxide film.

Of course, respective effects of cobalt and zinc can also be expected byadding cobalt and zinc in the ranges as mentioned above.

The alloy of the present invention can be die cast by the usual pressuredie casting method. Roughening of the surface of the die castingsobtained may be conveniently effected by the generally known methods.Selection of abrasive materials for blasting treatment, treating time,etc. can be optionally determined depending upon the surface state ofthe product .desired. Chemical brightening treatment is an essentialtreatment and its treatment may be effected by the generally knownmethods. The anodic oxide film of the die castings'subjected to no suchtreatment has a greyish black color and the desired film having lightuniform golden, yellowish brown, brown and reddish brown color tonecannot be obtained.

The die castings obtained in accordance with the method of the presentinvention are excellent in weathering resistance and corrosionresistance and can successfully be used for building materials,ornaments, etc. Even such products as of complicated three dimensionaldesign can be mass-produced at low cost by die casting methods.Therefore, it can be expected that the products will be highly utilizedfor building panels, houses, furnitures, utensils, vehicles, etc.

In the FIGURE, the area of quadrilateral ABCD shows the compositionranges of chromium and manganese in the alloy of the present inventionand the area of pentagonal DEFGH shows theoptimum composition ranges ofchromium and manganese in the alloy of the 1 present invention.

The Examples which follow illustrate but in no way limit the presentinvention.

, EXAMPLE] A die cast product was produced by die casting an aluminumalloy comprising 0.3 percent by weight of chromium, 0.5 percentby-weight of manganese, 0.12

percent by weight of iron, 0.07 percent by weight of silicon and thebalance being aluminum. Said product was subjected to sand blastingtreatment to render the surface completely aventurine. Thus treated, theprod-. uct was dipped in a chemical polishing solution comprising 70percent by weight of phosphoric acid, 3 percent by weight of nitric acidand the balance of water at a temperature of 95C for 90 seconds andthereafter rinsed with water. Then, the product was subjected toanodizing treatment in a 10 percent aqueous solution of sulfuric acid at20C under a current density of 2 A/dm for 30 minutes to obtain a uniformgolden col- 'ored film free from irregular patterns of metal flow, seamsand cold shuts on the. surface of the die cast product. Thus obtaineddie cast product had a Brinell hardness of H 27.

EXAMPLE 2 A die cast product was produced by die casting an aluminumalloy comprising 0.2 percent by weight of render the surface thereofcompletely aventurine. Thus treated, the product was subjected toelectro-polishing and then to anodizing treatment in a 15 percentaqueous solution of sulfuric acid at 20C under a current density of 2.0A/dm for minutes to form a uniform 4O reddish brown anodic oxide filmfree from irregular patterns of metal flow,seams and cold shuts on thedie cast product.

, E XAMPLE S3 13 The following Table 1 shows the Examples of the similarmethods with thoseofExarnples l and j Table 1 Compositions of alloy(wt%) Brinell Example hardness of No. die castings Cr Mn Co Zn Fc Si Al(H,,)

3 0.7 0.3 0. 13 0.07 balance 4 1.1 0.7 0.09 0.07 do. 5 0.3 0.5 0.5 0.1 10.08 do. 35 6 0.5 0.9 0.8 0.10 0.10 do. 7 0.2 1.9 0.6 0.10 0.05 do. 80.3 0.5 5.0 0.12 0.07 do. 31 9 0.9 1.1 3.0 0.10 0.05 do. 10 0.7 1.2 0.32.0 0.11 0.08 do. l 1 0.2 2.0 0.3 1.0 0.09 0.07 do. 12 0.2 0.6 0.5 2.00.10 0.06 do. 38 13 0.6 0.3 0.5 0.10

6 Pretreatment Anodizing treatment Color Thick- Elec- Current Electoneof ncss Roughening Brightentro density trolysisv anodic of ing lytc(A/dm time oxidc film (min) film (;1.)

Liquid chemical yellowhoning polishing H 80 2.0 30 ish Y brown aluminumparticle do. do. 1.0 do. 10 blasing steel shot do 10% blasting H 50 2.020 gold l3 do. do. do. 1.5 30 do. 15 aluminum particle do; 15% 2.0reddish 27 blasting H SO brown sand blasting do. 1 do. 2.0 30 gold 20aluminum yellowparticle electrodo. 3.0 10 i 9 blasting polishing brownsteel shot chemical do. 2.0 15 brown 10 blasting polishing y do. do. do.2.0 40 reddish 28 brown aluminum particle do. do. 2.0 20 gold 14 blasingchemical" treatment yellow: U for gaining I do. 2.0 15 ish l0ave'nturine surface brown The anodic oxide films obtained in the aboveExamples were all colored films free fromirregular patterns of metalflow, seams and cold shuts.

5. A method for forming a uniform, even, integral colored film onaluminum die castings, comprising:

subjecting the surface of an aluminum pressure die What is claimedis: 1. A method for forming a uniform, even, integral colored film onaluminum die castings, comprising:

subjecting the surface of an aluminum pressure die casting to a seriesof steps,

said aluminum casting comprising an aluminum alloy comprising 0.1-1.3percent by weight chromium; 0.2-3.4 percent by weight manganese;saidchromium and manganese present in amounts within the area ofquadrilateral ABCD shown in FIG. 1; up to 0.3 percent by weightimpurities; 0005-08 percent by weight cobalt; and the balance ofaluminum;

said steps comprising: 7

subjecting said aluminum pressure die casting to roughening treatment,

then subjecting said aluminum casting to brightening treatment,

and thereafter subjecting the aluminum casting to anodizing treatment inan aqueous electrolyte containing 5-20 percent by weight sulfuric acid,for forming an integral, uniform anodic oxide film having a colorselected from the group consisting of gold, yellowish brown, brown andreddish brown.

casting to a series of steps,

I said aluminum casting comprising an aluminum alloy comprising 0.1-1.3percent by weight chromium; 0.2-3.4 percent by weight manganese; saidchromium and manganese present in amounts within the area ofquadrilateral ABCD shown in FIG. 1; I up to 0.3 percent by weightimpurities; 0. l-5.0 percent by weight zinc; and the balance ofaluminum;

6.. The method according to claim 5, wherein the amounts of chromium andmanganese contained in said cent by weight iron.

4. The method according to claim 1, wherein said aluminum alloyadditionally comprises up to 0.1 percent by weight silicon.

aluminum alloy are within the area of pentagonal DEFGl-l shown inFIG. 1. 7. The method according to claim 5, wherein said aluminum alloyadditionally comprises up to 0.2 percent by weight iron.

, 8. The method according to claim 5, wherein said aluminum alloyadditionally comprises up to 0.1 percent by weight silicon.

9., A method according to claim 5, wherein said aluminum alloyadditionally contains 0.005-0.8 percent by weight of cobalt.

2. The method according to claim 1, wherein the amounts of chromium andmanganese contained in said aluminum alloy are within the area ofpentagonal DEFGH shown in FIG.
 1. 3. The method according to claim 1,wherein said aluminum alloy additionally comprises up to 0.2 percent byweight iron.
 4. The method according to claim 1, wherein said aluminumalloy additionally comprises up to 0.1 percent by weight silicon.
 5. Amethod for forming a uniform, even, integral colored film on aluminumdie castings, comprising: subjecting the surface of an aluminum pressuredie casting to a series of steps, said aluminum casting comprising analuminum alloy comprising 0.1-1.3 percent by weight chromium; 0.2-3.4percent by weight manganese; said chromium and manganese present inamounts within the area of quadrilateral ABCD shown in FIG. 1; up to 0.3percent by weight impurities; 0.1-5.0 percent by weight zinc; and thebalance of aluminum; said steps comprising: subjecting said aluminumpressure die casting to roughening treatment, then subjecting saidaluminum casting to brightening treatment, and thereafter subjecting thealuminum casting to anodizing treatment in an aqueous electrolytecontaining 5-20 percent by weight sulfuric acid, for forming anintegral, uniform anodic oxide film having a color selected from thegroup consisting of gold, yellowish brown, brown and reddish brown. 6.The method according to claim 5, wherein the amounts of chromium andmanganese contained in said aluminum alloy are within the area ofpentagonal DEFGH shown in FIG.
 1. 7. The method according to claim 5,wherein said aluminum alloy additionally comprises up to 0.2 percent byweight iron.
 8. The method according to claim 5, wherein said aluminumalloy additionally comprises up to 0.1 percent by weight silicon.
 9. Amethod according to claim 5, wherein said aluminum alloy additionallycontains 0.005-0.8 percent by weight of cobalt.